TEST
Stop-Signal Test (SST)
How long it takes the brain to cancel a response that has already been initiated
Stop-Signal Task with adaptive logic (Logan, 1994; Verbruggen et al., 2019). Estimates the SSRT, the internal latency of the inhibitory process: the cleanest metric available to quantify impulse control in milliseconds.
200
TRIALS
75/25
GO / STOP (%)
SSD
ADAPTIVE 50-900 ms
SSRT
INHIBITORY LATENCY
WHAT THE TEST IS
The gold standard of motor inhibitory control
Unlike the conventional Go/No-Go task—where the user knows in advance that they must withhold a response—the SST requires canceling a response that has already been initiated: the stop signal appears after a brief delay following the Go stimulus. This activates the neural substrate of reactive inhibitory control (right inferior frontal gyrus, subthalamic nuclei).
By applying the independent race model (Logan, 1994), it enables estimation of the Stop-Signal Reaction Time (SSRT): the internal latency of the inhibitory process, which is virtually inaccessible with any other paradigm. The adaptive SSD logic allows it to be administered to everyone from users with slowness to elite athletes, always keeping the successful inhibition rate close to the 50% required by the model.
HOW IT IS ADMINISTERED
Respond to the green arrow, stop when the red hand appears
A green arrow pointing left or right appears between two buttons; the user must press the indicated button as quickly as possible. In 25% of the trials, after a brief delay (SSD), the arrow changes to a red hand indicating that the response must be inhibited. Total: 200 trials (150 Go + 50 Stop).
The SSD starts at 250 ms and adjusts dynamically: +50 ms if the user inhibits correctly (it becomes more difficult), -50 ms if they fail (it becomes easier). This algorithm keeps the success rate at ~50%, a necessary condition for valid SSRT calculation. Any response made after the stop signal—or even before it, if the subject responded prematurely—is counted as an inhibition failure.
WHAT THE TEST MEASURES
Indicators and their interpretation
SSRT is the key metric, but it is only valid if the inhibition rate is close to 50% and the subject has not adopted a deliberate waiting strategy.
SSRT
Stop-Signal Reaction Time: estimated latency of the inhibitory process. The time it takes the brain to cancel an ongoing motor command.
Prolonged SSRT: slow inhibition (ADHD, Parkinson’s, schizophrenia).
Short SSRT: excellent reactive inhibitory control.
% correct inhibitions
Percentage of Stop trials in which inhibition was successful. It should be close to 50% for SSRT to be estimated reliably.
< 30%: massive failure or stimuli that are too fast.
> 70%: probable waiting strategy (inflated Go RT).
Go RT
Mean reaction time in trials without a stop signal. Helps separate general slowness from specific inhibitory deficit.
High Go RT + high SSRT: global slowing.
Normal Go RT + high SSRT: pure inhibitory deficit.
RT variability
Standard deviation of Go RT. Marker of attentional fluctuations and stability of activation level.
High variability: fluctuating attention (ADHD, TBI).
Low variability: consistent performance.
Mean SSD
Mean Stop-Signal Delay reached by the adaptive algorithm. Indicates how much delay the subject needs to inhibit at 50%.
High SSD: the subject inhibits well even with little advance warning.
Low SSD: requires a lot of advance warning to inhibit.
RT in failed stop trials
Mean time in Stop trials where inhibition was not achieved. Under valid conditions, it should be lower than Go RT (race model).
Stop RT ≪ Go RT: typical healthy pattern.
Stop RT ≈ Go RT: indication of model violation (unreliable data).
REFERENCES
Bibliography
- Logan, G. D., & Cowan, W. B. (1984). On the ability to inhibit thought and action: A theory of an act of control. Psychological Review, 91(3), 295–327.
- Verbruggen, F., Aron, A. R., Band, G. P. H., et al. (2019). A consensus guide to capturing the ability to inhibit actions and impulsive behaviors in the stop-signal task. eLife, 8, e46323.
- Aron, A. R., Robbins, T. W., & Poldrack, R. A. (2014). Inhibition and the right inferior frontal cortex: One decade on. Trends in Cognitive Sciences, 18(4), 177–185.
- Lipszyc, J., & Schachar, R. (2010). Inhibitory control and psychopathology: A meta-analysis of studies using the stop signal task. Journal of the International Neuropsychological Society, 16(6), 1064–1076.
- Obeso, I., Wilkinson, L., & Jahanshahi, M. (2011). Levodopa medication does not influence motor inhibition or conflict resolution in a conditional stop-signal task in Parkinson’s disease. Experimental Brain Research, 213(4), 435–445.
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The only task that directly estimates the time of the internal inhibitory process. Adaptive logic that works from cognitive slowness to elite athletes.
